System and method to diagnose fuel system pressure sensor

ABSTRACT

A system includes an ignition detection module, a pressure sensor, a pressure variation module, and a pressure sensor diagnostic module. The ignition detection module detects when an engine is started. The pressure sensor generates a first pressure signal indicating a first pressure within a fuel system of the engine when the engine is started and when a purge valve of the fuel system is closed. The pressure variation module determines an amount of variation in the first pressure signal over a first period. The pressure sensor diagnostic module determines a state of the pressure sensor based on the amount of variation in the first pressure signal over the first period.

FIELD

The present disclosure relates generally to vehicle diagnostic systemsand more particularly to a system and a method to diagnose a pressuresensor of a fuel system of a vehicle.

BACKGROUND

The background description provided here is for the purpose of generallypresenting the context of the disclosure. Work of the presently namedinventors, to the extent it is described in this background section, aswell as aspects of the description that may not otherwise qualify asprior art at the time of filing, are neither expressly nor impliedlyadmitted as prior art against the present disclosure.

Internal combustion engines combust an air and fuel mixture withincylinders to drive pistons, which produces drive torque. Air flow intothe engine is regulated via a throttle. More specifically, the throttleadjusts throttle area, which increases or decreases air flow into theengine. As the throttle area increases, the air flow into the engineincreases. A fuel control system adjusts the rate that fuel is injectedto provide a desired air/fuel mixture to the cylinders and/or to achievea desired torque output. Increasing the amount of air and fuel providedto the cylinders increases the torque output of the engine.

In spark-ignition engines, spark initiates combustion of an air/fuelmixture provided to the cylinders. In compression-ignition engines,compression in the cylinders combusts the air/fuel mixture provided tothe cylinders. Spark timing and air flow may be the primary mechanismsfor adjusting the torque output of spark-ignition engines, while fuelflow may be the primary mechanism for adjusting the torque output ofcompression-ignition engines.

SUMMARY

A system comprises an ignition detection module, a pressure sensor, apressure variation module, and a pressure sensor diagnostic module. Theignition detection module detects when an engine is started. Thepressure sensor generates a first pressure signal indicating a firstpressure within a fuel system of the engine when the engine is startedand when a purge valve of the fuel system is closed. The pressurevariation module determines an amount of variation in the first pressuresignal over a first period. The pressure sensor diagnostic moduledetermines a state of the pressure sensor based on the amount ofvariation in the first pressure signal over the first period.

In other features, the pressure variation module determines the amountof variation based on a difference between a current pressure readingand a previous pressure reading, an absolute value of the currentpressure reading and the previous pressure reading, and a running totalof the absolute value of the current pressure reading and the previouspressure reading over the first period.

In other features, the pressure sensor diagnostic module determines thatthe pressure sensor operates normally if the amount of variation in thefirst pressure signal is less than a first threshold and that thepressure sensor is faulty if the amount of variation in the firstpressure signal is greater than or equal to the first threshold. Thefirst threshold is determined based on a leakage rating of the purgevalve.

In other features, the pressure sensor subsequently generates a secondpressure signal indicating a second pressure within the fuel system whenthe purge valve of the fuel system is cycled at a duty cycle. Thepressure variation module determines an amount of variation in thesecond pressure signal over a second period. The system furthercomprises a purge flow diagnostic module that diagnoses a faultassociated with flow through the purge valve if the amount of variationin the first pressure signal is less than the first threshold and if theamount of variation in the second pressure signal is less than a secondthreshold.

In other features, the pressure variation module determines the amountof variation based on a difference between a current pressure readingand a previous pressure reading, an absolute value of the currentpressure reading and the previous pressure reading, and a running totalof the absolute value of the current pressure reading and the previouspressure reading over the second period.

In other features, the purge flow diagnostic module determines thesecond threshold based on a predetermined relationship between a flowrestriction in the purge valve and the amount of variation.

In other features, the purge flow diagnostic module adjusts the amountof variation based on an amount of boost provided to the engine duringthe second period.

In other features, the purge flow diagnostic module determines thesecond threshold based on an amount of boost provided to the engine.

In other features, the system further comprises a valve control modulethat controls the duty cycle of the purge valve at a predetermined valueduring the second period.

In other features, the system further comprises a vent valve controlmodule that opens a vent valve of the fuel system during the secondperiod.

In still other features, a method comprises detecting when an engine isstarted; generating, using a pressure sensor, a first pressure signalindicating a first pressure within a fuel system of the engine when theengine is started and when a purge valve of the fuel system is closed;determining an amount of variation in the first pressure signal over afirst period; and determining a state of the pressure sensor based onthe amount of variation in the first pressure signal over the firstperiod.

In other features, the method further comprises determining the amountof variation amount based on a difference between a current pressurereading and a previous pressure reading, an absolute value of thecurrent pressure reading and the previous pressure reading, and arunning total of the absolute value of the current pressure reading andthe previous pressure reading over the first period.

In other features, the method further comprises determining that thepressure sensor operates normally if the amount of variation in thefirst pressure signal is less than a first threshold and that thepressure sensor is faulty if the amount of variation in the firstpressure signal is greater than or equal to the first threshold, anddetermining the first threshold based on a leakage rating of the purgevalve.

In other features, the method further comprises subsequently generatinga second pressure signal indicating a second pressure within the fuelsystem when the purge valve of the fuel system is cycled at a dutycycle, determining an amount of variation in the second pressure signalover a second period, and diagnosing a fault associated with flowthrough the purge valve if the amount of variation in the first pressuresignal is less than the first threshold and if the amount of variationin the second pressure signal is less than a second threshold.

In other features, the method further comprises determining the amountof variation based on a difference between a current pressure readingand a previous pressure reading, an absolute value of the currentpressure reading and the previous pressure reading, and a running totalof the absolute value of the current pressure reading and the previouspressure reading over the second period.

In other features, the method further comprises determining the secondthreshold based on a predetermined relationship between a flowrestriction in the purge valve and the amount of variation.

In other features, the method further comprises adjusting the amount ofvariation based on an amount of boost provided to the engine during thesecond period.

In other features, the method further comprises determining the secondthreshold based on an amount of boost provided to the engine.

In other features, the method further comprises maintaining the dutycycle of the purge valve at a predetermined value during the secondperiod.

In other features, the method further comprises opening a vent valve ofthe fuel system during the second period.

Further areas of applicability of the present disclosure will becomeapparent from the detailed description, the claims and the drawings. Thedetailed description and specific examples are intended for purposes ofillustration only and are not intended to limit the scope of thedisclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a functional block diagram of an example engine systemaccording to the principles of the present disclosure;

FIG. 2 is a functional block diagram of an example control systemaccording to the principles of the present disclosure;

FIG. 3 is a flowchart illustrating an example control method accordingto the principles of the present disclosure;

FIG. 4 is a graph illustrating example pressure sensor signals accordingto the principles of the present disclosure;

FIGS. 5 and 6 are graphs illustrating example values for diagnosing flowthrough a purge valve according to the principles of the presentdisclosure; and

FIG. 7 is a graph illustrating an example of results of diagnostics of afuel system pressure sensor performed according to the presentdisclosure.

In the drawings, reference numbers may be reused to identify similarand/or identical elements.

DETAILED DESCRIPTION

A fuel system may include a fuel tank and an evaporative emissions(EVAP) system that collects fuel vapor from the fuel tank andselectively provides the fuel vapor to the engine, which combusts thefuel vapor. The EVAP system may include a canister, a vent valve, adiurnal control valve (on a sealed fuel system), and a purge valve. Thecanister adsorbs fuel vapor from a fuel tank. The vent valve allowsambient air to enter the canister when the vent valve is open. The purgevalve allows fuel vapor to flow from the canister to an intake system ofthe engine. A vacuum in the intake system may draw fuel vapor from thecanister to the intake system when the vent valve is open to allowairflow through the canister and the purge valve is open to allow thefuel vapor to enter the intake system. Thus, instead of venting fuelvapor from the fuel tank directly into the atmosphere, the fuel vapor iscombusted in the engine, which reduces emissions and improves fueleconomy.

A control system may perform a diagnostic to ensure that the EVAP systemis functioning properly. During the diagnostic, the control system mayclose the vent valve and open the purge valve to create a vacuum in thefuel system. The control system may then monitor pressure in the fuelsystem during a diagnostic period using a pressure sensor. If thepressure decreases by an amount that is less than a threshold,indicating that flow through the purge valve is insufficient, thecontrol system may diagnose a fault in the EVAP system.

If the engine is equipped with a boost device such as a turbocharger,the control system may not perform the diagnostic during boost operationdue to the amount time required to perform the diagnostic. During thediagnostic, the pressure in the sealed portion of the fuel system may bemonitored for a diagnostic period of 20 to 30 seconds to allow a vacuumto build up within the fuel system. However, boost operation may onlylast for a period of 5 to 10 seconds, and the results of the diagnosticmay not be reliable if the boost operation period ends before thediagnostic period ends.

In addition, during the diagnostic, the diagnostic system closes thevent valve to seal the canister from the atmosphere. Thus, atmosphericair is not allowed to flow through the canister, and therefore fuelvapor is not purged from the canister to the intake system during thediagnostic. As a result, performing the diagnostic may reduce the amountby which the EVAP system may reduce emissions and improve fuel economy.

Flow through a purge valve can be diagnosed based on a fuel systempressure sensor. Specifically, a variation in a signal generated by thepressure sensor can be determined. A fault associated with flow throughthe purge valve can be diagnosed based on the pressure variation. Thepurge valve opens and closes at a frequency with an opening period thatis based on a duty cycle of the purge valve. As the purge valve opensand closes, flow through the purge valve causes changes in the pressuresignal. However, if there is a flow restriction in the purge valve, thepressure signal may not vary as much as expected based on the duty cycleof the purge valve. A fault associated with flow through the purge valvemay be diagnosed when the pressure variation is less than a threshold.The threshold may be determined based on a predetermined relationshipbetween a flow restriction in the purge valve and the pressurevariation.

The pressure signal may be monitored for a relatively short period(e.g., one second) to determine the pressure variation. The diagnosticmay be performed to evaluate flow through the purge valve during boostoperation. In addition, the vent valve may be open or closed when thesystem and method performs the diagnostic. Thus, performing thediagnostic may not reduce the amount by which the EVAP system may reduceemissions and improve fuel economy.

In some instances, the fuel system pressure sensor may be noisy. Forexample, the fuel system pressure sensor may generate electrical noise.Alternatively or additionally, the fuel system pressure sensor may besubjected to noise generated by engine firing. The noise may affect thereliability of the EVAP purge flow diagnostic. For example, a noisy fuelsystem pressure sensor may falsely indicate that the EVAP system ispurging and that the purge flow diagnostic passed when in fact the EVAPsystem is not purging due to a failure in the EVAP system.

A system and method according to the present disclosure perform adiagnostic of the fuel system pressure sensor when the vehicle isstarted and purging is yet to begin. Specifically, when the vehicle isstarted and before purging begins, the system and method determines avariation in a signal generated by the pressure sensor. The system andmethod determines if the variation is less than or equal to apredetermined threshold. If the variation is less than a threshold, thepressure sensor is determined to be not noisy and reliable to performsubsequent EVAP purge flow diagnostic. If the variation is greater thanor equal to the threshold, the pressure sensor is determined to benoisy, not reliable to perform subsequent EVAP purge flow diagnostic,and must be replaced.

Referring to FIG. 1, an engine system 100 includes an engine 102 thatcombusts an air/fuel mixture to produce drive torque for a vehicle basedon driver input from a driver input module 104. The driver input may bebased on a position of an accelerator pedal. The driver input may alsobe based on a cruise control system, which may be an adaptive cruisecontrol system that varies vehicle speed to maintain a predeterminedfollowing distance.

Air is drawn into the engine 102 through an intake system 108. Theintake system 108 includes an intake manifold 110 and a throttle valve112. For example only, the throttle valve 112 may include a butterflyvalve having a rotatable blade. An engine control module (ECM) 114controls a throttle actuator module 116, which regulates opening of thethrottle valve 112 to control the amount of air drawn into the intakemanifold 110.

Air from the intake manifold 110 is drawn into cylinders of the engine102. While the engine 102 may include multiple cylinders, forillustration purposes a single representative cylinder 118 is shown. Forexample only, the engine 102 may include 2, 3, 4, 5, 6, 8, 10, and/or 12cylinders. The ECM 114 may instruct a cylinder actuator module 120 toselectively deactivate some of the cylinders, which may improve fueleconomy under certain engine operating conditions.

The engine 102 may operate using a four-stroke cycle. The four strokes,described below, are named the intake stroke, the compression stroke,the combustion stroke, and the exhaust stroke. During each revolution ofa crankshaft (not shown), two of the four strokes occur within thecylinder 118. Therefore, two crankshaft revolutions are necessary forthe cylinder 118 to experience all four of the strokes.

During the intake stroke, air from the intake manifold 110 is drawn intothe cylinder 118 through an intake valve 122. The ECM 114 controls afuel actuator module 124, which regulates fuel injection to achieve adesired air/fuel ratio. Fuel may be injected into the intake manifold110 at a central location or at multiple locations, such as near theintake valve 122 of each of the cylinders. In various implementations,fuel may be injected directly into the cylinders or into mixing chambersassociated with the cylinders. The fuel actuator module 124 may haltinjection of fuel to cylinders that are deactivated.

The injected fuel mixes with air and creates an air/fuel mixture in thecylinder 118. During the compression stroke, a piston (not shown) withinthe cylinder 118 compresses the air/fuel mixture. The engine 102 may bea compression-ignition engine, in which case compression in the cylinder118 ignites the air/fuel mixture. Alternatively, the engine 102 may be aspark-ignition engine, in which case a spark actuator module 126energizes a spark plug 128 in the cylinder 118 based on a signal fromthe ECM 114, which ignites the air/fuel mixture. The timing of the sparkmay be specified relative to the time when the piston is at its topmostposition, referred to as top dead center (TDC).

The spark actuator module 126 may be controlled by a timing signalspecifying how far before or after TDC to generate the spark. Becausepiston position is directly related to crankshaft rotation, operation ofthe spark actuator module 126 may be synchronized with crankshaft angle.In various implementations, the spark actuator module 126 may haltprovision of spark to deactivated cylinders.

Generating the spark may be referred to as a firing event. The sparkactuator module 126 may have the ability to vary the timing of the sparkfor each firing event. The spark actuator module 126 may also be capableof varying the spark timing for a next firing event when the sparktiming signal is changed between a last firing event and the next firingevent. In various implementations, the engine 102 may include multiplecylinders and the spark actuator module 126 may vary the spark timingrelative to TDC by the same amount for all cylinders in the engine 102.

During the combustion stroke, the combustion of the air/fuel mixturedrives the piston down, thereby driving the crankshaft. The combustionstroke may be defined as the time between the piston reaching TDC andthe time at which the piston returns to bottom dead center (BDC). Duringthe exhaust stroke, the piston begins moving up from BDC and expels thebyproducts of combustion through an exhaust valve 130. The byproducts ofcombustion are exhausted from the vehicle via an exhaust system 134.

The intake valve 122 may be controlled by an intake camshaft 140, whilethe exhaust valve 130 may be controlled by an exhaust camshaft 142. Invarious implementations, multiple intake camshafts (including the intakecamshaft 140) may control multiple intake valves (including the intakevalve 122) for the cylinder 118 and/or may control the intake valves(including the intake valve 122) of multiple banks of cylinders(including the cylinder 118). Similarly, multiple exhaust camshafts(including the exhaust camshaft 142) may control multiple exhaust valvesfor the cylinder 118 and/or may control exhaust valves (including theexhaust valve 130) for multiple banks of cylinders (including thecylinder 118).

The cylinder actuator module 120 may deactivate the cylinder 118 bydisabling opening of the intake valve 122 and/or the exhaust valve 130.In various implementations, the intake valve 122 and/or the exhaustvalve 130 may be controlled by devices other than camshafts, such aselectromagnetic or electrohydraulic actuators.

The time at which the intake valve 122 is opened may be varied withrespect to piston TDC by an intake cam phaser 148. The time at which theexhaust valve 130 is opened may be varied with respect to piston TDC byan exhaust cam phaser 150. A phaser actuator module 158 may control theintake cam phaser 148 and the exhaust cam phaser 150 based on signalsfrom the ECM 114. When implemented, variable valve lift may also becontrolled by the phaser actuator module 158.

The engine system 100 may include a boost device that providespressurized air to the intake manifold 110. For example, FIG. 1 shows aturbocharger including a hot turbine 160-1 that is powered by hotexhaust gases flowing through the exhaust system 134. The turbochargeralso includes a cold air compressor 160-2, driven by the turbine 160-1,that compresses air leading into the throttle valve 112. In variousimplementations, a supercharger (not shown), driven by the crankshaft,may compress air from the throttle valve 112 and deliver the compressedair to the intake manifold 110.

A wastegate 162 may allow exhaust to bypass the turbine 160-1, therebyreducing the boost (the amount of intake air compression) of theturbocharger. The ECM 114 may control the turbocharger via a boostactuator module 164. The boost actuator module 164 may modulate theboost of the turbocharger by controlling the position of the wastegate162. In various implementations, multiple turbochargers may becontrolled by the boost actuator module 164. The turbocharger may havevariable geometry, which may be controlled by the boost actuator module164.

An intercooler (not shown) may dissipate some of the heat contained inthe compressed air charge, which is generated as the air is compressed.The compressed air charge may also have absorbed heat from components ofthe exhaust system 134. Although shown separated for purposes ofillustration, the turbine 160-1 and the compressor 160-2 may be attachedto each other, placing intake air in close proximity to hot exhaust.

The engine 102 combusts fuel provided by a fuel system 166. The fuelsystem 166 includes a fuel tank 168, a canister 170, a vent valve 172, apurge valve 174, check valves 176, and a jet pump 177. The canister 170adsorbs fuel from the fuel tank 168. The vent valve 172 allowsatmospheric air to enter the canister 170 when the vent valve 172 isopen. The purge valve 174 allows fuel vapor to flow from the canister170 to the intake system 108 when the purge valve 174 is open. The checkvalves 176 prevent flow from the intake system 108 to the canister 170.The ECM 114 controls a valve actuator module 178, which regulates thepositions of the vent valve 172 and the purge valve 174. The ECM 114 mayopen the vent valve 172 and the purge valve 174 to purge fuel vapor fromthe canister 170 to the intake system 108.

Fuel vapor flows from the canister 170 to the intake system 108 througha first flow path 179 a or a second flow path 179 b. When the boostdevice is operating (e.g., when the wastegate 162 is closed), thepressure at the outlet of the first flow path 179 a is less than thepressure at the outlet of the second flow path 179 b. Thus, fuel vaporflows from the canister 170 to the intake system 108 through the firstflow path 179 a. When the boost device is not operating (e.g., when thewastegate 162 is open), the pressure at the outlet of the first flowpath 179 a is greater than the pressure at the outlet of the second flowpath 179 b. Thus, fuel vapor flows from the canister 170 to the intakesystem 108 through the second flow path 179 b.

When the boost device is operating, the pressure of intake air upstreamfrom the compressor 160-2 is less than the pressure of intake airdownstream from the compressor 160-2. The jet pump 177 utilizes thispressure difference to create a vacuum that draws fuel vapor from thecanister 170 into the intake system 108. The fuel vapor flows throughthe jet pump 177 and enters the intake system 108 upstream from thecompressor 160-2.

The engine system 100 may measure the position of the crankshaft using acrankshaft position (CKP) sensor 180. The temperature of the enginecoolant may be measured using an engine coolant temperature (ECT) sensor182. The ECT sensor 182 may be located within the engine 102 or at otherlocations where the coolant is circulated, such as a radiator (notshown).

The pressure within the intake manifold 110 may be measured using amanifold absolute pressure (MAP) sensor 184. In various implementations,engine vacuum, which is the difference between ambient air pressure andthe pressure within the intake manifold 110, may be measured. The massflow rate of air flowing into the intake manifold 110 may be measuredusing a mass air flow (MAF) sensor 186. In various implementations, theMAF sensor 186 may be located in a housing that also includes thethrottle valve 112.

The throttle actuator module 116 may monitor the position of thethrottle valve 112 using one or more throttle position sensors (TPS)190. The temperature of ambient air being drawn into the engine 102 maybe measured using an intake air temperature (IAT) sensor 192. Thepressure of ambient air being drawn into the engine 102 may be measuredusing an ambient air pressure (AAP) sensor 194. The pressure within thefuel system 166 may be measured using a fuel system pressure (FSP)sensor 196. The FSP sensor 196 may generate a signal 197 indicating thefuel system pressure. The FSP sensor 196 may be located in a line 198extending between the canister 170 and the purge valve 174, as shown, orin the canister 170. The ECM 114 may use signals from the sensors tomake control decisions for the engine system 100.

The ECM 114 may also perform a diagnostic to evaluate flow through thepurge valve 174. The ECM 114 may determine a variation in the signal 197generated by the FSP sensor 196 and diagnose a fault associated withflow through the purge valve 174 based on the pressure variation. TheECM 114 may diagnose the fault when the pressure variation is less thana threshold. The ECM 114 may set a diagnostic trouble code (DTC) and/oractivate a service indicator 199 when the fault is diagnosed. Theservice indicator 199 indicates that service is required using a visualmessage (e.g., text), an audible message (e.g., chime), and/or a tactilemessage (e.g., vibration).

Referring to FIG. 2, an example implementation of the ECM 114 includesan engine speed module 202, an engine vacuum module 204, a desired purgeflow module 206, a valve control module 208, a pressure variation module210, a purge flow diagnostic module 212, an ignition detection module214, and a pressure sensor diagnostic module 216. The engine speedmodule 202 determines engine speed. The engine speed module 202 maydetermine the engine speed based on the crankshaft position from the CKPsensor 180. For example, the engine speed module 202 may determine theengine speed based on a period of crankshaft rotation corresponding to anumber of tooth detections. The engine speed module 202 outputs theengine speed.

The engine vacuum module 204 determines engine vacuum. The engine vacuummodule 204 may determine engine vacuum based on the manifold pressurefrom the MAP sensor 184 and the atmospheric pressure from the AAP sensor194. The difference between the manifold pressure and the atmosphericpressure may be referred to as engine vacuum when the manifold pressureis less than the atmospheric pressure. The difference between themanifold pressure and the atmospheric pressure may be referred to asboost when the manifold pressure is greater than the atmosphericpressure. The engine vacuum module 204 outputs the engine vacuum (orboost).

The desired purge flow module 206 determines a desired amount of flowthrough the purge valve 174. The desired purge flow module 206 maydetermine the desired purge flow based on the engine vacuum and/or theengine speed. The desired purge flow module 206 outputs the desiredpurge flow.

The valve control module 208 outputs a signal to the valve actuatormodule 178 to control the positions of the vent valve 172 and the purgevalve 174. The valve control module 208 may output a duty cycle tocontrol the position of the purge valve 174. For example, when the dutycycle is set at 25 percent, the purge valve 174 may be open for 25percent of the time and off for 75 percent of the time. The valvecontrol module 208 may ramp up or ramp down the duty cycle to achievethe desired purge flow.

The pressure variation module 210 determines a variation in the signal197 generated by the FSP sensor 196. As discussed above, the signal 197indicates the fuel system pressure. The pressure variation module 210may determine the pressure variation based on a running total of anabsolute difference between a previous pressure reading and a presentpressure reading. For example, the pressure variation module 210 maydetermine a present pressure variation (PV)prs based on the presentpressure reading (PR)prs, the previous pressure reading (PR)prv, and aprevious pressure variation (PV)prv using a relationship such as(PV)prs=|PRprs−PRprv|+(PV)prv  (1)

The purge flow diagnostic module 212 diagnoses a fault associated withflow through the purge valve 174 based on the pressure variation over adiagnostic period (e.g., one second). The purge flow diagnostic module212 may diagnose the fault based on the pressure variation over multiplediagnostic periods (e.g., five one-second periods). The purge flowdiagnostic module 212 may perform the diagnostic when the boost deviceis operating or when the boost device is not operating. The purge flowdiagnostic module 212 may output a signal indicating when the diagnosticperiod begins and ends. The valve control module 208 may maintain theduty cycle of the purge valve 174 at a predetermined percentage (e.g., apercentage within a range from 25 percent to 75 percent) during thediagnostic period. The valve control module 208 may open or close thevent valve 172 during the diagnostic period.

The purge flow diagnostic module 212 may diagnose the fault when thepressure variation is less than a threshold, indicating that arestriction of flow through the purge valve 174 is greater than adesired amount. The purge flow diagnostic module 212 may set a DTC whenthe fault is diagnosed. The purge flow diagnostic module 212 mayactivate the service indicator 199 when the DTC is set during twodifferent ignition cycles. During one ignition cycle, an ignition system(not shown) is switched from off to on (or run) and then returned tooff. The purge flow diagnostic module 212 may determine the thresholdbased on a relationship between the flow restriction in the purge valve174 and the pressure variation. The relationship may be predeterminedthrough empirical testing by determining the pressure variation atvarious known amounts of flow restriction.

The pressure variation may be affected by the boost. For example, for agiven amount of flow restriction in the purge valve 174, the pressurevariation may be greater when the boost is relatively high than when theboost is relatively low. The purge flow diagnostic module 212 may adjustthe pressure variation based on the boost. For example, the purge flowdiagnostic module 212 may normalize the pressure variation with respectto the boost. In turn, the purge flow diagnostic module 212 may use thesame threshold to diagnose the fault at different levels of boost.Alternatively, the purge flow diagnostic module 212 may determine thethreshold based on the boost.

The pressure sensor diagnostic module 216 diagnoses the FSP sensor 196over a diagnostic period when the engine is started to ensure that thesubsequently performed purge flow diagnostics when the vehicle isoperated are reliable. Specifically, the ignition detection module 214detects when the engine is started (i.e., ignition is turned on). Atthis time, purge flow control is not turned on, the duty cycle of thepurge valve 174 is zero, and the purge valve 173 is closed.

The pressure sensor diagnostic module 216 determines a variation in thesignal 197 generated by the FSP sensor 196 over the diagnostic period.As discussed above, the signal 197 indicates the fuel system pressure.The pressure variation module 210 may determine the pressure variationbased on a running total of an absolute difference between a previouspressure reading and a present pressure reading. For example, thepressure variation module 210 may determine a present pressure variation(PV)prs based on the present pressure reading (PR)prs, the previouspressure reading (PR)prv, and a previous pressure variation (PV)prvusing a relationship such as(PV)prs=|PRprs−PRprv|+(PV)prv  (1)

The pressure sensor diagnostic module 216 determines that the FSP sensor196 operates normally (e.g., with acceptable noise level so as to beable to provide reliable purge flow diagnostics) if the amount ofvariation in the signal 197 over the diagnostic period is less than apredetermined threshold. The pressure sensor diagnostic module 216determines that the FSP sensor 196 is faulty (e.g., with unacceptablenoise level so as to be unable to provide reliable purge flowdiagnostics) if the amount of variation in the signal 197 is greaterthan or equal to the predetermined threshold.

The predetermined threshold is determined based on a leakage rating ofthe purge valve 173. For example, according to established standards,the worst-case (i.e., maximum allowable) leakage rating of the purgevalve 173 may be 0.020. Accordingly, the predetermined threshold may bedetermined based on a leakage rating of 0.020 or 0.040.

The pressure sensor diagnostic module 216 generates a signal at the endof the diagnostic period to indicate a status of the FSP sensor 196determined based on the diagnostics performed as above over thediagnostic period. For example, the pressure sensor diagnostic module216 may generate a signal to indicate that the FSP sensor 196 is faultyif the amount of variation in the signal 197 is greater than or equal tothe predetermined threshold.

The pressure sensor diagnostic module 216 may also provide the signal tothe purge flow control module 212 at the end of the diagnostic period.The purge flow control module 212 may suspend the purge flow diagnosticsif the FSP sensor 196 is faulty and may perform the purge flowdiagnostics only if the FSP sensor 196 operates normally. Subsequent todetermining that the FSP sensor 196 operates normally, the purge flowcontrol module 212 may perform the purge flow diagnostics as describedabove, the results of the purge flow diagnostics are reliable. When theFSP sensor 196 is diagnosed to be faulty, the FSP sensor 196 must bereplaced or the purge flow diagnostics performed using the faulty FSPsensor 196 may be unreliable.

The diagnostics of the FSP sensor 196 performed as described above whenthe engine is started and before purge flow control begins may providemany benefits. Without the diagnostics, a noisy FSP sensor 196 mayfalsely pass the EVAP purge flow diagnostics. The diagnostics of the FSPsensor 196 involve a quick pass/fail decision, increase purge flowvolume and can be performed without any additional hardware (e.g., afuel tank isolation valve).

Without the diagnostics of the FSP sensor 196 described above,alternatives may include not using the EVAP purge flow diagnostics basedon the variation method described above. Alternatively, a fuel tankisolation valve can be added between fuel tank and canister so that whenthe isolation valve is commanded to be closed, the volume on the EVAPsystem is reduced to only canister volume plus lines. Without theisolation valve, the time to build vacuum is much greater than 10seconds. If a fuel tank isolation valve is used, however, fuel tankisolation valve diagnostics may be needed. Alternatively, a CanisterVent Solenoid (CVS) can be commanded to be closed while under boostedoperation, and sufficient vacuum can be created in the sealed canister.In contrast, the diagnostics of the FSP sensor 196 described above notonly do not require any of these alternative, but also make thesubsequent EVAP purge flow diagnostics nonintrusive (CVS is open).

Referring to FIG. 3, an example of a method 250 for diagnosing a FSPsensor and subsequently reliably diagnosing a fault associated with flowthrough a purge valve of a fuel system is shown. At 252, the methoddetermines whether the engine is turned on. The method waits until theengine is turned on. At 254 after the engine is turned on, the methodstarts a diagnostic period. At 256, with the purge valve closed andbefore purge flow diagnostics and control begin, the method performs FSPsensor diagnostics. For example, the method may perform the FSP sensordiagnostics using relationship (1) discussed above. At 258, the methoddetermines if the diagnostic period ended. The method returns to 256 ifthe diagnostic period has not yet ended. At 260, if the diagnosticperiod has ended, the method determines based on the diagnosticsperformed whether the FSP sensor is faulty. At 262, if the FSP sensor isfaulty, the method lights a service indicator to indicate that the FSPsensor is faulty.

After diagnosing the FSP sensor, the fuel system provides fuel to theengine, which may be equipped with a boost device such as aturbocharger. At 304, the method determines whether to start adiagnostic period to perform EVAP purge flow diagnostics. The method maystart the diagnostic period when the boost device is operating or whenthe boost device is not operating. The method waits until the diagnosticperiod starts.

At 306, after the diagnostic period starts, the method monitors enginevacuum. The method may determine engine vacuum based on a differencebetween pressure within an intake manifold of the engine and atmosphericpressure. The difference between the manifold pressure and theatmospheric pressure may be referred to as engine vacuum when themanifold pressure is less than the atmospheric pressure. The differencebetween the manifold pressure and the atmospheric pressure may bereferred to as boost when the manifold pressure is greater than theatmospheric pressure.

At 308, the method monitors pressure within the fuel system. The methodmay measure the fuel system pressure using a pressure sensor thatgenerates a signal indicating the fuel system pressure. At 310, themethod maintains a duty cycle of a purge valve of the fuel system at apredetermined percentage (e.g., a percentage within a range from 25percent to 75 percent). In addition, the method may open or close a ventvalve of the fuel system during the diagnostic period.

At 312, the method determines a variation of the signal generated by thepressure sensor. The method may determine the pressure variation basedon a running total of an absolute difference between a previous pressurereading and a present pressure reading. For example, the method maydetermine the pressure variation using relationship (1) discussed above.At 314, the method adjusts the pressure variation based on amount ofboost provided to the engine during the diagnostic period. For example,the method may normalize the pressure variation with respect to theboost.

At 316, the method determines whether to stop the diagnostic period. Themethod may stop the diagnostic period when a predetermined period (e.g.,one second) elapses after the method starts the diagnostic period. Ifmethod decides to stop the diagnostic period, the method continues at318. Otherwise, the method continues at 306. In various implementations,the method may determine the pressure variation over multiple diagnosticperiods (e.g., five one-second periods).

At 318, the method determines whether the pressure variation is lessthan a threshold. The method may determine the threshold based on arelationship between the flow restriction in the purge valve and thepressure variation. The relationship may be predetermined throughempirical testing by determining the pressure variation at various knownamounts of flow restriction. The method may also determine the thresholdbased on the boost when, for example, the pressure variation is notnormalized with respect to the boost. If the pressure variation is lessthan the threshold, the method continues at 320. Otherwise, the methodcontinues at 304.

At 320, the method diagnoses a fault associated with a flow restrictionin the purge valve. The method may set a DTC when the fault isdiagnosed. The method may activate a service indicator when the DTC isset during two different ignition cycles. The detection of the faultassociated with the flow restriction in the purge valve may be reliableif the FSP sensor diagnostics passed. The detection of the faultassociated with the flow restriction in the purge valve may beunreliable if the FSP sensor diagnostics failed.

Referring to FIG. 4, examples of signals that may be generated by a fuelsystem pressure sensor during a one-second diagnostic period are shownat 402, 404, 406, and 408. The signals 402, 404, 406, and 408 areplotted with respect to an x-axis 410 and a y-axis 412. The x-axis 410represents time in seconds. The y-axis 412 represents unitlessmagnitudes of the signals.

The variation of each of the signals 402, 404, 406, and 408 may bedetermined using relationship (1) discussed above. If relationship (1)is used to determine the variations, the variations of the signals 402,404, 406, and 408 are 0, 1, 4, and 16, respectively. Thus, the variationdetermined using relationship (1) increases as the amount of change orvariation in the signals 402, 404, 406, and 408 increases.

Referring to FIG. 5, a first set of pressure variation amounts 502 and asecond set of pressure variation amounts 504 are plotted with respect toan x-axis 506 and a y-axis 508. The x-axis 506 represents engine vacuumin kilopascals (kPa). The y-axis 508 represents the pressure variationper second. Since the values along the x-axis 506 are all negative, thex-axis 506 may be referred to as representing the amount of boostprovided to an engine. The boost amount is equal in magnitude to thevalues along the x-axis 506, but is opposite in polarity.

The pressure variation amounts 502 correspond to a first amount of flowrestriction within a purge valve. In this example, a purge flow pathwithout any flow restriction has a diameter of 0.197 inches (in) and across-sectional area of 0.0304 square inches (in²), and the first amountof flow restriction has a cross-sectional area of 0.0182 in². Thus, thepurge flow path as restricted by the first amount of flow restrictionhas a diameter of 0.125 in and a cross-sectional area of 0.0123 in². Thefirst amount of flow restriction may correspond to a worst performingacceptable amount of purge flow.

The pressure variation amounts 504 correspond to a second amount of flowrestriction within the purge valve. The second amount of flowrestriction is has a cross-sectional area of 0.0292 in². Thus, the purgeflow path as restricted by the second amount of flow restriction has adiameter of 0.040 in and a cross-sectional area of 0.001 in². The secondamount of flow restriction may correspond to a best performingunacceptable amount of purge flow.

A best fit line 510 through the pressure variation amounts 502 may beobtained using linear regression. A threshold for diagnosing a purgeflow fault may be determined by subtracting an offset from the best fitline 510. Since the pressure variation amounts 502 increase as the boostincreases, the threshold may also increase as the boost increases.

Referring to FIG. 6, a first set of pressure variation amounts 602 and asecond set of pressure variation amounts 604 are plotted with respect toan x-axis 606 and a y-axis 608. The x-axis 606 represents engine vacuumin kPa. The y-axis 608 represents the pressure variation per second.Since the values along the x-axis 606 are all negative, the x-axis 606may be referred to as representing the amount of boost provided to anengine. The boost amount is equal in magnitude to the values along thex-axis 606, but is opposite in polarity.

The pressure variation amounts 602, 604 are obtained by normalizing thepressure variation amounts 502, 504 of FIG. 5 with respect to boost. Thepressure variation amounts 502, 504 are normalized by dividing thepressure variation amounts 502, 504 by their respective best fit lines.A threshold 610 for diagnosing a purge flow fault is determined byadding an offset to a best fit line of the pressure variation amounts604. For example, the threshold 610 may be equal to a sum of an averageof the pressure variation amounts 502 and a product of a multiplier(e.g., 4) and the standard deviation of the pressure variation amounts502. Since the pressure variation amounts 602, 604 are normalized withrespect to boost, a single-value threshold (e.g., 0.3) may be used todiagnose a fault associated with flow through a purge valve regardlessof the boost amount.

Referring to FIG. 7, an example of results of FSP sensor diagnosticsperformed according to the present disclosure are shown. A first set ofpressure variation amounts 702 and a second set of pressure variationamounts 704 are plotted with respect to an x-axis 706 and a y-axis 708.The x-axis 706 represents engine vacuum in kPa. The y-axis 708represents the pressure variation per second as sensed by. A threshold710 is based on a permissible leakage through the purge valve.

If the FSP sensor diagnostics result in the first set of pressurevariation amounts 702 that are greater than the threshold 710, the FSPsensor is noisy and must be replaced. The EVAP purge flow diagnosticsand control subsequently performed using the noisy FSP sensor may beunreliable. If the FSP sensor diagnostics result in the second set ofpressure variation amounts 704 that are less than the threshold 710, theFSP sensor operates normally. The EVAP purge flow diagnostics andcontrol subsequently performed using the FSP sensor are reliable.

The foregoing description is merely illustrative in nature and is in noway intended to limit the disclosure, its application, or uses. Thebroad teachings of the disclosure can be implemented in a variety offorms. Therefore, while this disclosure includes particular examples,the true scope of the disclosure should not be so limited since othermodifications will become apparent upon a study of the drawings, thespecification, and the following claims. As used herein, the phrase atleast one of A, B, and C should be construed to mean a logical (A or Bor C), using a non-exclusive logical OR. It should be understood thatone or more steps within a method may be executed in different order (orconcurrently) without altering the principles of the present disclosure.

In this application, including the definitions below, the term modulemay be replaced with the term circuit. The term module may refer to, bepart of, or include an Application Specific Integrated Circuit (ASIC); adigital, analog, or mixed analog/digital discrete circuit; a digital,analog, or mixed analog/digital integrated circuit; a combinationallogic circuit; a field programmable gate array (FPGA); a processor(shared, dedicated, or group) that executes code; memory (shared,dedicated, or group) that stores code executed by a processor; othersuitable hardware components that provide the described functionality;or a combination of some or all of the above, such as in asystem-on-chip.

The term code, as used above, may include software, firmware, and/ormicrocode, and may refer to programs, routines, functions, classes,and/or objects. The term shared processor encompasses a single processorthat executes some or all code from multiple modules. The term groupprocessor encompasses a processor that, in combination with additionalprocessors, executes some or all code from one or more modules. The termshared memory encompasses a single memory that stores some or all codefrom multiple modules. The term group memory encompasses a memory that,in combination with additional memories, stores some or all code fromone or more modules. The term memory may be a subset of the termcomputer-readable medium. The term computer-readable medium does notencompass transitory electrical and electromagnetic signals propagatingthrough a medium, and may therefore be considered tangible andnon-transitory. Non-limiting examples of a non-transitory tangiblecomputer readable medium include nonvolatile memory, volatile memory,magnetic storage, and optical storage.

The apparatuses and methods described in this application may bepartially or fully implemented by one or more computer programs executedby one or more processors. The computer programs includeprocessor-executable instructions that are stored on at least onenon-transitory tangible computer readable medium. The computer programsmay also include and/or rely on stored data.

What is claimed is:
 1. A system comprising: a pressure sensor thatgenerates a first pressure signal indicating a first pressure within afuel system of an engine when the engine is started and when a purgevalve of the fuel system is closed; and a controller configured to:detect when the engine is started, determine an amount of variation inthe first pressure signal over a first period, determine a state of thepressure sensor based on the amount of variation in the first pressuresignal over the first period, and determine that the pressure sensoroperates normally if the amount of variation in the first pressuresignal is less than a first threshold and that the pressure sensor isfaulty if the amount of variation in the first pressure signal isgreater than or equal to the first threshold, wherein the firstthreshold is determined based on a leakage rating of the purge valve,and wherein the leakage rating of the purge valve is non-zero.
 2. Thesystem of claim 1 wherein the controller is configured to determine theamount of variation in the first pressure signal based on a differencebetween a current pressure reading and a previous pressure reading, anabsolute value of the difference between the current pressure readingand the previous pressure reading, and a running total of the absolutevalue of the difference between the current pressure reading and theprevious pressure reading over the first period.
 3. The system of claim1 wherein the pressure sensor subsequently generates a second pressuresignal indicating a second pressure within the fuel system when thepurge valve of the fuel system is cycled at a duty cycle, wherein thecontroller is configured to determine an amount of variation in thesecond pressure signal over a second period, and wherein the controlleris further configured to: diagnose a fault associated with flow throughthe purge valve if the amount of variation in the first pressure signalis less than the first threshold and the amount of variation in thesecond pressure signal is less than a second threshold.
 4. The system ofclaim 3 wherein the controller is configured to determine the amount ofvariation in the second pressure signal based on a difference between acurrent pressure reading and a previous pressure reading, an absolutevalue of the difference between the current pressure reading and theprevious pressure reading, and a running total of the absolute value ofthe difference between the current pressure reading and the previouspressure reading over the second period.
 5. The system of claim 3wherein the controller is configured to determine the second thresholdbased on a predetermined relationship between a flow restriction in thepurge valve and the amount of variation in the second pressure signal.6. The system of claim 3 wherein the controller is configured to adjustthe amount of variation in the second pressure signal based on an amountof boost provided to the engine during the second period.
 7. The systemof claim 3 wherein the controller is configured to determine the secondthreshold based on an amount of boost provided to the engine.
 8. Thesystem of claim 3 wherein the controller is further configured tocontrol the duty cycle of the purge valve at a predetermined valueduring the second period.
 9. The system of claim 3 wherein thecontroller is further configured to open a vent valve of the fuel systemduring the second period.
 10. A method comprising: detecting when anengine is started; generating, using a pressure sensor, a first pressuresignal indicating a first pressure within a fuel system of the enginewhen the engine is started and when a purge valve of the fuel system isclosed; determining an amount of variation in the first pressure signalover a first period; determining a state of the pressure sensor based onthe amount of variation in the first pressure signal over the firstperiod; determining that the pressure sensor operates normally if theamount of variation in the first pressure signal is less than a firstthreshold and that the pressure sensor is faulty if the amount ofvariation in the first pressure signal is greater than or equal to thefirst threshold; and determining the first threshold based on a leakagerating of the purge valve, wherein the leakage rating of the purge valveis non-zero.
 11. The method of claim 10 further comprising determiningthe amount of variation in the first pressure signal based on adifference between a current pressure reading and a previous pressurereading, an absolute value of the difference between the currentpressure reading and the previous pressure reading, and a running totalof the absolute value of the difference between the current pressurereading and the previous pressure reading over the first period.
 12. Themethod of claim 10 further comprising: subsequently generating a secondpressure signal indicating a second pressure within the fuel system whenthe purge valve of the fuel system is cycled at a duty cycle;determining an amount of variation in the second pressure signal over asecond period; and diagnosing a fault associated with flow through thepurge valve if the amount of variation in the first pressure signal isless than the first threshold and the amount of variation in the secondpressure signal is less than a second threshold.
 13. The method of claim12 further comprising determining the amount of variation in the secondpressure signal based on a difference between a current pressure readingand a previous pressure reading, an absolute value of the differencebetween the current pressure reading and the previous pressure reading,and a running total of the absolute value of the difference between thecurrent pressure reading and the previous pressure reading over thesecond period.
 14. The method of claim 12 further comprising determiningthe second threshold based on a predetermined relationship between aflow restriction in the purge valve and the amount of variation in thesecond pressure signal.
 15. The method of claim 12 further comprisingadjusting the amount of variation in the second pressure signal based onan amount of boost provided to the engine during the second period. 16.The method of claim 12 further comprising determining the secondthreshold based on an amount of boost provided to the engine.
 17. Themethod of claim 12 further comprising maintaining the duty cycle of thepurge valve at a predetermined value during the second period.
 18. Themethod of claim 12 further comprising opening a vent valve of the fuelsystem during the second period.